Has it got to be drivable on the road or a full race YB engine.
Mine is a road engine with ports , valves, cams all well off race spec it will be circa 700bhp on race Fuel. Assume over 800bhp abtainable if a few more comprimises are made with roadability.
You can always cheat , mine also has a 200bhp Nitrous capability. A 1000bhp YB engine exists in Cyprus using Nitrous.